Artemisia annua L., also know as Sweet Wormwood, is an annual herb that belongs to the wormwood family Artemisia. Artemisinin, a sequiterpene lactone compound that contains a peroxide bridge structure, is isolated form the above-ground portion of the Artemisia annua L. plant. Presently, artemisinin is recognized worldwide as the most effective pharmaceutical drug for malaria, especially for cerebral malaria and chloroquine-resistant malaria. Amorpha-4,11-diene synthase (Ads) is a key enzyme in the synthesis pathway of artemisinin, as well as an important target for bio-engineering of artemisinin metabolism. Using genetic engineering tools, in particular, antisense RNA to suppress the expression of the ads gene, will lead to Artemisia annua L. plants that do not produce artemisinin or produce less artemisinin. Due to the redistribution of the metabolism stream to the synthesis of secondary metabolites such as other terpenes, those Artemisia annua L. plants will have increased production of those secondary metabolites.
Patchoulol (patchouli alcohol) is commonly known in China as Bye Cho Lee alcohol. It has a molecular weight of 222 and its melting point is between 55° C.-59° C. The molecular formula of patchouli alcohol is C15H26O. It dissolves easily in organic solvents such as ethanol, acetone, petroleum ether, but not in water. Patchouli alcohol is a natural monomer with a special fragrant smell. It is extracted from Pogostemon cablin and used for fragrance and perfume. As defined by French Standard Committee, patchouli alcohol is a significant component in fragrance. It can also be used to treat fungal skin diseases or serve as starting materials for the synthesis of other synthetic compounds. Thus, increasing patchouli alcohol production has a significant commercial value as well as broad market prospects. As a key enzyme in the synthesis pathway of patchouli alcohol in Pogostemon cablin, Pts is an important target for bio-engineering of patchouli alcohol metabolism. Applying genetic engineering tools to generate Artemisia annua L. plants transformed with the key enzyme pts gene can overcome the “bottleneck” speed limit during patchouli alcohol biosynthesis. Such high-yield Artemisia annua L. plants provide a new approach for large-scale production of patchouli alcohol.
In an article entitled “Redirection of Cytosolic or Plastidic Isoprenoid Precursors Elevates Terpene Production in Plants” (Nature Biotechnology, vol. 24, p 1441-1447, 2006), Joe Chappell and colleagues report that, through over-expression of patchoulol synthase, transgenic tobacco plants can produce patchouli alcohol, which is not normally produced by tobacco plants. Moreover, the patchouli alcohol content reaches 0.5 microgram in every gram of wet-weight material. Therefore, it is possible to produce patchouli alcohol in plants that normally do not produce this compound, through metabolic regulation of the key steps of the patchouli alcohol synthesis pathway.
However, there are no currently available technologies in the literature that relate to increasing the patchouli alcohol content by utilizing the pts gene and RNA interference of the ads gene.